DE10230331B3 - Assembly, for injection molding shaped foam bodies, has an intermediate store with pressure control for plasticized plastics between the extruder and the injector - Google Patents

Abstract

The assembly to produce foamed bodies has an extruder (10) with a foaming agent feed (20). An intermediate store (40) is between the extruder and the injection unit (50), for injection molding, to be filled with plasticized plastic material during the injection action into the mold (60). A control system (44,46) sets the pressure within the intermediate store. The assembly to produce foamed bodies has an extruder (10) with a foaming agent feed (20). An intermediate store (40) is between the extruder and the injection unit (50), for injection molding, to be filled with plasticized plastic material during the injection action into the mold (60). A control system (44,46) sets the pressure within the intermediate store. A pressure sensor is within the intermediate store, or in the connecting channel (32) between the extruder and the store.

Description

The invention relates to a Apparatus and a method for the manufacture of foamed plastic articles.

From the DE 1 142 229 C It is known to provide between an extruder and an injection cylinder a pressure accumulator in the form of a piston-cylinder arrangement. During the injection in this arrangement the extruder can be continuously operated, since the plastic material can be collected during the injection in the cylinder space of the pressure accumulator, the piston is displaced by the pressure of the conveyed from the extruder the plastic material against spring force or gas force.

On the other hand, it can also with continuous Operation of the extruder, irregularities in the promotion the plastic material coming, for example, due to a backlog, because when you inject the flow path is interrupted injection cylinder or because the inertia and friction of the piston in the pressure accumulator can be overcome got to. Here can cause harm sensitive plastic materials, such as blowing agents offset plastic masses come.

In the from WO 98/31521 A1 and DE 19934693 A1 known devices is plasticized plastic material in an extruder, and the plasticized plastic material is a Treibbmittel added. The material is then fed into an injection cylinder from which it is injected after filling of the cylinder into a mold.

Over the from the DE 10055022 A1 known device is plasticized plastic material in an extruder, passed through a mixer and collected in a dwell and release space. This dwell and release space, by means of a slider or the like to be completed, and forms an injection cylinder in which the plasticized and leavened plastic material by means of a piston-cylinder unit can be held under a predeterminable pressure and from which it by means of the piston cylinder - Unit can be injected into a mold.

Because during the injection of the Injection cylinder in the known devices for manufacturing of foamed Plastic items are not charged with plastic material can, the are extruder operated discontinuously, which when stopping or Starting to pressure variations and, thus damage can lead to sensitive plastic material.

Accordingly, the invention lies The object of an apparatus and a method for producing of foamed to provide plastic articles, in which a careful treatment the plastic materials is ensured.

This object is achieved by a device according to claim 1 or by a method according to claim 5 solved; the dependent claims relate to advantageous developments of the invention.

According to the invention, the extruder continuously with a while of the injection process can be filled to operate latch, wherein the regulated pressure of the accumulator is. This allows a physical blowing agent or a reactive Blowing agents are incorporated at constant pressure. So that is the use of any blowing agent in principle in the desired States of matter, for example gaseous and not supercritical, possible. In particular, it is possible to carry out pressure control of the buffer to a level at the not yet expanded the plastic material.

A tightly closing shut-off device is preferred or relief element provided according to the plasticizing unit to Troubleshooting in plasticizing a pressure drop in the plasticized To avoid material in the accumulator piston and / or the injection cylinder.

An embodiment of the invention is based on the attached Drawing explains in schematic, partially broken away side view of a device according to the invention shows.

The device comprises a twin-screw extruder with a screw cylinder 10 In which two axially parallel screw 16 . 18 axially immovably rotatably are mounted. Via a screw conveyor 13 and a funnel 14 is plastic material from a dosing station 12 inserted into the inside of the screw barrel and by rotating the screws 10 plasticized means of a drive and conveyed towards a discharge end at which the screw cylinder 10 in a connecting line 32 empties. Between the hopper 14 and the ejection end of the cylinder is a propellant supply station 20 provided the propellant in the form of gas by means of a pump 8th introduces into the preferably already plasticized plastic material from a gas reservoir. Here, the use has the advantage of not axially displaceable screw, that the blowing agent is always introduced into the plastics material at the same location of the processing path. This is in contrast to devices with injection screw in which the screw moves during plasticizing, so that the effective screw length downstream of the intake for the propellant varies. The constant introduction of the blowing agent leads to this in comparison a homogenization of the melt quality.

The connecting line 32 terminates in a latch 40 Ie a plenum 47 a storage cylinder 45 In which an accumulator piston 42 is slidably received. The gathering room 47 is over a line 70 with a plenum 46 an injection piston-cylinder arrangement 50 connected.

During operation, plastic material is continuously conveyed from the extruder and fills the collecting space 56 the arrangement 50 , the piston 54 is displaced from the flowing plastic mass or withdrawn in a controlled manner. When the collection chamber 56 is filled to a predetermined extent with plastic material, the connection between the buffer 40 and the injection cylinder arrangement 50 a locking member 72 interrupted, and the plasticized plastic mass is from the piston 52 , Which by a drive 58 is operated in a form 60 injected.

At the same time of the buffer is collected in the collection chamber 40 the plastic material continuously supplied by the extruder. The piston is used to ensure constant pressure conditions 42 the cache 40 connected to a displacement device. The shifting device comprises two piston-cylinder arrangements 44 and 46 Wherein the respective pistons via a connecting member 48 with the piston 45 the cache 40 are connected. By loading the pistons of the piston cylinder units 44 . 46 with a pressure medium, the piston can be moved and move accordingly via the link 48 the piston 42 the cache 40 , The arrangement is preferably such that the displacement direction, a defined force on the piston of the latch 40 exercise, so that the plasticized plastic material is in the buffer memory at a defined pressure, that the pistons of the displacement means are acted upon in the figure from the top with pressure means. In other applications, it may be useful to move the piston of the cache active upwards so that in this case the pistons 44 . 46 are acted upon from below by pressure means.

The displacement of the piston 42 (not shown) depending on the signals of a pressure sensor controlled in the intermediate memory or, preferably, in the course of the line 32 is arranged. The control is preferably done so that a pressure is maintained, wherein the propellant is provided with plastic compound is not expanding. The arrangement of the pressure sensor in the conduit 32 has the advantage that pressure variations caused by the extruder, can be detected early, and the piston 40 can be moved correspondingly early.

In the course of the line 32 Furthermore, a locking and release member 30 arranged with which the connection between the discharge opening of the extruder and the buffer 40 can be interrupted. If it is supplied, for example due to a fault in the extruder with plastics material at low pressure or may not be further processed for a malfunction in the injection unit of plastic material and the capacity of the buffer is reached, locks the body 30 the connection so that the plastic material downstream of the organ 30 by means of the buffer 40 is maintained at the required pressure. Here, the organ 30 with a derivative of 34 be provided, is removed via the nachgefördertes plastic material from the system, for example in a water bath 74 ,

The blocking and relief body 30 comprises a body 31 , in the one hand the ejection end of the screw cylinder 10 opens, on the other hand the connection line 32 , In the body 31 is a pestle 33 slidably provided with a piston-cylinder unit 35 connected is. From a hydraulic fluid pump 39 becomes hydraulic fluid through lines 36 or 37 fed to the piston-cylinder unit so that the plunger 33 corresponding to a position of the control valve 38 can be moved. The arrangement is preferably such that the plunger can be adjusted into a first position in which the discharge end of the screw cylinder 10 with the derivative 34 and at least one second position in which the organ 30 the discharge end of the screw cylinder 10 to the connecting line 32 combines. In addition, a further position can be provided in which the plunger 33 the ejection end of the screw cylinder 10 closes.

To start up the system, the plunger can be moved initially in its first position, so that initially produced plastic material is discharged from the system. The initially obtained plastic material has in fact not yet have the required consistency and / or composition that is achieved only during continuous operation of the extruder usually at the beginning. As soon as the material has the desired consistency, which is reflected by empirical values. Observation of the leaking plastic material and / or measurements reveals the organ 30 so that the further resulting plastic material is fed into the latch moved to its open position. It is also possible for the organ 35 to move into a closed position, which supports the pressure build-up in the extruder.

Preferably, the organ is 30 abängig also operated by the signals of the pressure sensor to an excessive pressure build-up or a pressure drop downstream counteract the extruder.

Preferably, the blocking and relief means is 30 Further, in connection with the dosing station 12 operated. For example, that Outsize relief element 30 be moved into the discharge position, when it is detected by a controller, that via the dosing 12 an incorrect mixture of raw materials is fed. In this case, the plasticized plastic mass is not the desired composition and can be correspondingly derived from the system is achieved through proper dosing.

Details about the drives to be used and about a control device for the buffer 40 as well as for the locking and release member 30 are not given here because their implementation is familiar to the person skilled in the art.

Claims (5)

Device for producing foamed plastic articles, with an extruder ( 10 ) Having a blowing agent supply ( 20 has), with an injection unit ( 50 ), With an intermediate extruder ( 10 ) And injection unit ( 50 ) arranged intermediate storage that can be filled during the injection process ( 40 ) for plasticized plastic material, as well as with a device ( 44 . 46 ) For regulating the pressure in the buffer ( 40 ). Apparatus according to claim 1, characterized by a pressure sensor which in the intermediate store ( 40 ) or in a connection ( 32 ) is arranged between the extruder and the buffer. Device according to claim 1 or 2, characterized in that the intermediate store is a piston-cylinder arrangement ( 42 . 45 ) For storing the plastic material and a drive ( 44 . 46 has) for the controlled displacement of the piston. Device according to one of claims 1 to 3, with a pressure-controlled lock or relief means ( 30 ) in a connection ( 32 ) between extruders ( 10 ) and buffer ( 40 ). A process for the manufacture of foamed plastic articles, in which the plastic material continuously plasticized and mixed, and is added to the plastic material with a blowing agent during mixing, the plastics material batchwise into a mold ( 60 ) Injects and collects upon injection at the same time accumulating plastics material in a buffer, and wherein one regulates the pressure of the plastic material in the intermediate storage.